App Freezer
Select apps to freeze from list of all apps. Quick freezing achieved by a click of a button, and the frozen app will not restart unless you launch the frozen app! (Several apps like Facebook will restart as this is allowed by Android OS)

It’s free — with In-App Purchases. I have to wonder what those might be.

Still, would this work with the Insignia Flex Elite 7.85 and prevent standby battery drain by telling certain apps to shut up? Or would those apps be invisible to this without root?

It won’t work on system apps for sure and also no apps with broadcast receivers that restarts on several different events. You would need root, Xposed Framework and perhaps the experimental functions in Greenify to be able to stop all that. AJK Labs even say that themselves in the app description on Play. I checked because I got curious to how they would ever be able to freeze system apps and apps like Facebook (with broadcast receivers) without root and Xposed. It turns out they can’t.

Sorry, I’ll be faster next time. But as I never heard of that app before I wasn’t sure if they actually found a way to freeze things without root permissions. It sounded too good to be true and it turned out that it was. Even with root, Xposed and developer tools it’s very hard to shut down all wake on broadcast in some apps. Cut off too many and the app won’t start. Like a booby trap, which is intentional of course. Except for the Chinese communication app QQi with 67 permissions no apps I know of have more permissions than Facebook (59) and FB Messenger (48). There’s no end to how these apps track the users. I can only guess why QQi has all these permissions…